Chip-core framework for systems-on-a-chip

ABSTRACT

A system-on-chip interconnection structure and method uses unidirectional buses only, central shared memory controllers, separate interconnects for high-speed and low-speed peripherals, zero wait-state register accesses, application-specific memory map and peripherals, application-specific test methodology, allowances for cache controllers, and good fits with standard ASIC flow and tools.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of the earlier filed U.S. Provisional application Ser. No. 60/176,921, filed Jan. 20, 2000, which is incorporated by reference for all purposes into this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to flexible modular integrated circuit embodiments, and more specifically to a structured framework for constructing and interfacing variable mixtures of computer processors, memories, peripherals, and other functional modules on a single semiconductor integrated circuit.

2. Description of the Prior Art

As systems-on-chip (SoC) become more complex, it will be increasingly difficult for a single company to provide its customers with all of the intellectual-property (IP) cores and library macrocells they require. Companies have to evaluate whether human resources, capital and time are expendable on extraneous developments. A growing trend is to outsource the areas that fall outside of their core competencies.

Time-to-market is the dominant factor directing this make vs. buy decision. SoCs are reaching higher levels of integration, but their complexity is inversely proportional to the allowable time-to-market. “Buying” semiconductor IP will become essential for surviving in an environment that demands increased profits and decreased time-to-market. For companies to meet the technology challenges of integrating externally developed semiconductor IP into a single chip, within the given time window, they will have to partner with others, including, in some cases, their competitors.

Outsourcing and partnership will be the essential elements of a successful semiconductor business in the next century because those capabilities will help companies deliver what customers want. Companies using SoC technologies have recognized the need to license or buy IP from other companies. But just purchasing the IP is not enough. Integrating IP in a system-on-chip is complicated, especially when components from multiple sources are involved. IP integrators and providers need to actively work together to make sure that all of the pieces of the SoC fit seamlessly. One way to leverage the strength of a partnership is by offering an open architecture.

Successful semiconductor companies must be able to deliver to the customer an on-chip architecture, in which components can be dropped in and interconnected with little difficulty. Open means that it is supported by third-party companies, thereby producing a collaborative effort to reduce the design-integration struggles found in SoC development, including hardware and software codesign and coverification. That also results in reducing time-to-market. Customers will have choices in how they build their SoC devices, which IP components to integrate, and what software and operating system to implement. Outsourcing and partnership are keys to successfully offering customers what they want. Taking this a step further, providing and/or supporting an open architecture gives customers the flexibility they need.

The electronics industry has been driven by the need to increase performance, reduce costs and enhance features. Many of these needs have been met through the use of newer, faster and cheaper technologies. Newer technologies continue to allow for more functions and features to be placed on a single piece of silicon. Functions that previously were placed on separate chips can now be integrated in a system-on-chip with new functions added.

In any processor-driven embodiment, a number of peripheral devices are needed. These include timers, DMA engines, interrupt controllers and memory controllers. In many cost-sensitive applications, a shared memory structure is preferably used to reduce memory component costs. An architecture is needed which addresses the memory needs of all devices without severely degrading the performance of any single device.

The PCIbus, ISA, VMEbus, and most other buses were designed as, system level buses to connect discrete devices on a printed circuit board (PCB) substrate. At the board level, a key issue is minimizing the number of bus signals because pin and signal count translate directly into package and PCB costs. A large number of device pins increases package footprint and reduces component density on the board. System level buses must support add-in cards and PCB backplanes where connector size and cost are also directly related to signal count. This is why traditional system level buses use shared tri-state signaling and, in the case of PCIbus, multiplexed address and data on the same signals. Timing problems can be investigated in the lab using prototype PCBs that can then be modified and re-spun in a few days.

In the on-chip world, signal routing consumes silicon area but does not affect the size or cost of packages, PCBs and connectors. The limited capabilities of today's logic synthesis tools directly impact embodiment time and performance and must be taken into account. Getting the lowest possible routing overhead is of little value if the system design time balloons way out of proportion and the market window is missed. Synthesis tools find it difficult to deal with shared tri-state signals with several drivers and receivers connected to the same trace. Static timing analysis is preferably awkward, and often the only way to verify timing is to use a circuit level simulator such as Spice. All of this takes time and effort without adding real value in terms of device functionality or features. Bus loading also limits theoretical performance and the verification problems associated with bus loading can lead to a conservative embodiment whose performance falls short of the inherent technology capabilities.

The on-chip world has a significantly different set of embodiment constraints and tradeoffs compared with the board-level environment. A bus designed for use on PCBs will not provide the most efficient on-chip solution. When we started the embodiment of our GreenLite hard disk controller core we quickly realized that we needed to create a completely new bus architecture optimized for systems-on-silicon. The key issues were performance, embodiment time reduction, ease of use, power consumption and silicon efficiency. The following sections describe embodiments of the present invention and show how we satisfied these requirements.

SUMMARY OF THE PRESENT INVENTION

It is therefore an object of the present invention to provide a system-on-chip interconnection structure and method for efficient integration of a variety of functional circuits.

It is a further object of the present invention to provide an on-chip interconnect architecture that standardizes how systems-on-chip are fabricated on silicon semiconductor integrated circuit chips.

Briefly, a system-on-chip interconnection structure and method embodiment of the present invention uses unidirectional buses only, central shared memory controllers, separate interconnects for high-speed and low-speed peripherals, zero wait-state register accesses, application-specific memory map and peripherals, application-specific test methodology, allowances for cache controllers, and good fits with standard ASIC flow and tools.

An advantage of the present invention is that a system is provided that enables electronics applications to be developed quickly and to be portable between silicon foundries.

Another advantage of the present invention is that a system is provided that can run at higher clock speeds.

These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the-art after having read the following detailed description of the preferred embodiment which is illustrated in the drawings.

IN THE DRAWINGS

FIG. 1 is a functional block diagram of an on-chip interconnect architecture embodiment of the present invention for system-on-chip integration;

FIG. 2 is a functional block diagram of a multi-processor hierarchy embodiment of the present invention;

FIG. 3 is a timing diagram of a p-bus write protocol embodiment of the present invention;

FIG. 4 is a timing diagram of a p-bus read protocol embodiment of the present invention;

FIG. 5 is a timing diagram of a p-bus write, with asynchronous wait, protocol embodiment of the present invention;

FIG. 6 is a timing diagram of a p-bus read, with asynchronous wait, protocol embodiment of the present invention;

FIG. 7 is a timing diagram of a p-bus write, with synchronous wait, protocol embodiment of the present invention;

FIG. 8 is a timing diagram of a p-bus read, with synchronous wait, protocol embodiment of the present invention;

FIG. 9 is a functional block diagram of a UART embodiment of the present invention;

FIG. 10 is a timing diagram of an m-bus non-burst write protocol embodiment of the present invention;

FIG. 11 is a timing diagram of an m-bus non-burst read protocol embodiment of the present invention;

FIG. 12 is a timing diagram of an m-bus read-modify-write protocol embodiment of the present invention;

FIG. 13 is a timing diagram of an m-bus memory burst write protocol embodiment of the present invention;

FIG. 14 is a timing diagram of an m-bus memory burst read protocol embodiment of the present invention;

FIG. 15 is a functional block diagram of an m-bus logical AND-OR connection embodiment of the present invention;

FIG. 16 is a functional block diagram of a Von Neuman processor embodiment of the present invention;

FIG. 17 is a functional block diagram of a Harvard processor embodiment of the present invention;

FIG. 18 is a functional block diagram of a dual processor embodiment of the present invention;

FIG. 19 is a functional block diagram of a dual processor and shared p-bus embodiment of the present invention;

FIG. 20 is a functional block diagram of a memory controller embodiment of the present invention;

FIG. 21 is a functional block diagram of a switched channel memory controller embodiment of the present invention;

FIG. 22 is a functional block diagram of a switched channel memory controller embodiment of the present invention;

FIG. 23 is a functional block diagram of a switched channel memory controller and dual processor embodiment of the present invention;

FIG. 24 is a functional block diagram of a configuration and control CPU embodiment of the present invention;

FIG. 25 is a functional block diagram of a shared PCIbus and no-processor embodiment of the present invention;

FIG. 26 is a functional block diagram of a configuration and control sequencer embodiment of the present invention;

FIG. 27 is a functional block diagram of an ARM7 embodiment of the present invention; and

FIG. 28 is a functional block diagram of a PCIbus embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an on-chip interconnect architecture embodiment of the present invention for system-on-chip integration, and is referred to by the general reference numeral 100. The system-on-chip interconnect architecture 100 comprises a single semiconductor chip 102 that may be externally interfaced to a shared memory bus 104 with memory such as a flash memory 106 and SDRAM 108. A CPU subsystem 110 includes a CPU core 112 and a local RAM-ROM memory 114. A CPU bus 116 interfaces these to a p-bus interface controller 118 which hosts several peripheral blocks, including DMA blocks 134 and 138 and non-DMA blocks 120 and 122 connected to a peripheral bus (p-bus) 124. A cache 126 and channel controller 128 interface the CPU bus 116 to a memory bus (m-bus) 130. Another m-bus channel controller 132 interfaces to DMA-block 134. Other such DMA interfaces between the m-bus 130 and p-bus 124 are represented by a channel controller 136 and DMA-block 138. A MAC 140 connects the shared memory bus 104 to the internal m-bus 130 and p-bus 124 with the aid of a bus arbiter 142.

The system-on-chip interconnect architecture 100 preferably enables electronics applications to be developed quickly and to be portable between silicon foundries. Embodiments of architecture 100 must be easily synthesizable, centered around shared memory, flexible, modular, not sacrifice performance over alternative approaches, and must not add to embodiment cost. Therefore, embodiments of architecture 100 are constructed, in general, with unidirectional buses only, central shared memory controllers, separate interconnects for high-speed and low-speed peripherals, zero wait-state register accesses, application-specific memory map and peripherals, application-specific test methodology, allowances for cache controllers, and good fits with standard ASIC flow and tools.

The system-on-chip interconnect architecture 100 separates I/O control, data DMA and CPU onto separate buses to avoid bottlenecks. Architecture 100 includes the use of bus speeds that are scalable to technology and embodiment requirements. It supports 32-bit, 16-bit and 8-bit peripherals, it separates peripheral input/output (I/O) and direct memory access (DMA) interconnects, it uses simple protocols for reduced gate counts, uses positive-edge clocking only, uses no tri-state signals or bus holders, keeps itself to low capacitive loading for high performance operation, does single clock cycle data transfers, uses hidden arbitration for DMA bus masters so no additional clock cycles are needed for the arbitration, includes DMA channels with buffers (FIFOs) for addressing memory, its peripherals do not need to integrate FIFOs to interface to a DMA channel, has a channel structure that reduces latency while enhancing reusability and portability, has channels with closer ties to the memory controller through the m-bus, and includes on-chip memory for exclusive use of the processor via the processor's native bus.

The p-bus 124 provides for low-speed accesses to peripherals, while the m-bus 130 allows for high-speed accesses to shared memory from the CPU core 112 and peripherals. The p-bus 124 is the communications interface between the CPU and its peripherals, and is not used to access memory. The p-bus 124 is a master-slave interface with the CPU core 112 connected through an interface controller 118 as its single master. Its signal timing is synchronous with the CPU core 112. The MAC 140, arbiter 142 and channels (e.g., 132, 136) may also be tied to the p-bus 124 for configuration, control and status.

The m-bus 130 is the communications interface between the MAC 140 and the DMA channels (e.g., 132, 136). The m-bus 130 is preferably an arbitrated initiator-target interface with only one target, the MAC 140. Each initiator, or master, arbitrates for command of the MAC 140. Once a transfer is granted, the MAC 140 becomes the bus master and thereafter controls all the data flow. The m-bus 130 is synchronous to the MAC 140 and can facilitate peer-to-peer communications. But it is optimally used for peripheral-to-memory and memory-to-peripheral communications.

The CPU core 112 may be provided by a silicon foundry as a hardcore (e.g., ARM7, ARM9, MIPS, PowerPC, etc.) or by a core vendor as a soft core (e.g. ARM7TDMI-S, Lexra or ARC). The interface specifications for such must be provided. The preferred clock rate applied to the CPU core 112 depends on the p-bus 124 clock rate. It may be a divide-by-two of the p-bus 124 clock signal when the processor cannot be run at full system speed, or in order to guarantee a clock with a fifty percent duty cycle to the CPU. The CPU core clock can also be run at the same speed as the system to make everything fully synchronous and for performance.

All internal memory that is preferably used exclusively by the processor is connected directly to the CPU core 112 on its native buses. Address latching may be required. If no wait states are needed, then interface logic is minimal. The interface controller 118 generates a clock signal for the CPU and provides timing translation; blocks 120, 122, 134 and 138 address decode, and wait generation. The channel controllers 132 and 136 interface between any DMA peripherals and the m-bus 130. A peripheral block 134 or 138 interfaces to a channel only if it accesses shared memory. If a peripheral block 134 or 138 is asynchronous to the MAC 140, a buffer (FIFO) is implemented where the block's 134 or 138 side of the buffer is synchronous to the block's 134 or 138 clock signal. The MAC 140 side of the buffer is made synchronous to the MAC 140. The MAC 140 is preferably a target of the m-bus 130, and controls accesses to shared memory. Such includes all timing and protocol controls. Its interface to the arbiter 142 may be direct or through the m-bus 130, or with connections to both.

The arbiter 142 is generally application specific. It takes requests from each of the channels and responds with a grant when an access can be accommodated. It may be directly connected the MAC 140.

In general, each of the blocks 120, 122, 134 and 138 is preferably attached to the p-bus 124. Blocks that are generally needed in processor-based systems but which are not part of the CPU core 112 are attached to the p-bus 124. Examples of such blocks are timers, interrupt controllers and UARTs. If a peripheral block 134 and 138 performs DMA accesses to shared memory, it includes a p-bus 124 interface and a channel controller 132 and 136 to the m-bus 130.

An embodiment hardware development kit (PALM-CF2000) marketed by Palmchip Corporation (San Jose, Calif.) includes the peripheral components required for an ARM7TDMI system-on-chip embodiment. It includes a p-bus controller, m-bus bridge, DMA channel interfaces, system timer, watchdog timer, interrupt controller and memory controller. Such kit also includes a UART that may be used for software debug and system monitoring. New peripherals can be added and pre-existing functions ported to the p-bus and m-bus. Variations on the interface controller 118 and cache 126 can be made to support other CPU cores. For more information, see Palmchip's products web page at http://www.palmchip.com. Palmchip's PalmBeach development kit includes a development board, Gatefield FPGA toolkit, ARM software development toolkit and ARM7TDMI with JTAG embedded ICE for ARM. The HDK peripherals are preloaded into a Gatefield FPGA leaving room for 100 K gates of custom logic and space on the board for analog chips and connectors. Memory types supported are EDO DRAM, SDRAM, flash memory and EPROM. All ARM7, memory, embodiment interface, GPIO and UART port signals are visible.

Embodiments of the present invention preferably support ATPG and synchronous scan insertion done after a first netlist's simulation has been proved with test vectors. Scan insertion is then done and functional test vectors are rerun on the embodiment.

FIG. 2 illustrates a more complex example with more than one processor. A multi-processor system 200 includes, for example, a digital signal processor (DSP) core 202 connected to a private DSP-bus 204. A memory 206, a cache 208, and a p-bus controller 210 all interface to the DSP-bus 204. A p-bus 212 is common to other processors such as a CPU core 214. A private CPU-bus 216 is connected to a p-bus controller 218, a memory 222, and a cache 224. The p-bus is interfaced to several blocks represented by a pair of blocks 226 and 228. A DMA controller 230 is associated with a refresh controller 232 and several channel controllers 234, 236, and 238, on an m-bus 240. A memory access controller 242 is controlled by a bus arbiter 244 and will allow connections with an external memory bus 246. External memory units are represented by a pair of memories 248 and 250.

One cache 224 is illustrated with a channel interface 238 and the other cache 208 interfaces directly with m-bus 240. One processor memory DMA 222 is shown with a direct fill DMA channel 236 and the other memory 206 is not. Block 228 is shown with channel interface 234 to external shared memory 248 and 250, and block 226 has no such interface.

The p-buses 124 (FIG. 1) and 212 communicate between their CPUs and other peripherals, and are synchronous to the respective CPU. P-buses preferably support zero-wait-state accesses, and have data and address widths that are application-specific. The p-buses 124 (FIG. 1) and 212 include a master-slave interface that can support a single CPU master or multiple CPU masters. Its timings are synchronous with the CPU core, operating at a preferred clock signal rate that is equal to or twice the CPU clock signal rate.

The p-bus signals fall into two general categories, signals that are broadcast from the interface controller to all blocks, and “blk” signals that are sent point-to-point between the controller and a specific block. See Tables I and II. The prefix “pb” is specific to the p-bus embodiments of the present invention.

TABLE I p-bus signal summary signal direction required timing description pb_clk n/a yes n/a p-bus clock, equal to or twice CPU interface clock pb_addr cntlr-to- yes early, address to blks first 30% write or read of clk cycle pb_wdata cntlr-to- yes for early, write data blks write-only first 30% from CPU and of clk read/write cycle block pb_re cntlr-to- yes at least early, synchronous read blks one for read- first 30% enable for data in only, and of clk flip-flops read/write cycle block pb_rs cntlr-to- yes at least mid, asynchronous blks one for read- first 60% read only, and of clk strobe for data read/write cycle in flip-flops block pb_we cntlr-to- yes at least early, synchronous write blks one for read- first 30% enable for data only, and of clk in flip-flops read/write cycle block pb_ws cntlr-to- yes at least mid, write strobe for blks one for read- first 60% asynchronous only, and of clk data read/write cycle in flip-flops block pb_blk_sel cntlr-to- yes early, read or write blk first 30% block select of clk cycle pb_blk_rdata blk-to- yes at least late, read data to CPU cntlr one for read- first 70% only and of clock read/write cycle block pb_blk_wait blk-to- no early, wait cntlr first 30% of clk cycle

TABLE II p-bus signal descriptions pb_clk All signals are synchronous to the pb_clk. This is a clock signal that is p-bus clock preferably used by the p-bus controller. The pb_clk signal signal can be either the same frequency or twice the frequency of the CPU clock signal, depending on the target application and chip vendor process. High performance embodiments requiring a system clock signal which is running faster (up to two times) than the maximum speed of the processor can use the pb_clk running at twice the CPU clock signal frequency. In other systems where the processor can run on a same frequency as the system, pb_clk can match the CPU clock signal frequency. The pb_clk signal may be generated and distributed by the p-bus controller, or may be generated by a clock signal control module and distributed to the p-bus controller and other modules. pb_addr The p-buses 124 and 212 address is the address of a p-bus memory-mapped memory location (memory, register, address FIFO, etc.) that a CPU wishes to access. It is shared for reads and writes, and is broadcast to all blocks. It becomes valid on the rising edge of pb_clk when a pb_blk_sel is “1” pb_wdata The p-bus write data is the data to be written p-bus write to a memory-mapped memory location (memory, register, FIFO, etc.) by. It is preferably used only for writes and is broadcast to all blocks. It becomes valid on the rising edge of pb_clk when a pb_blk_sel and the corresponding pb_ws or pb_we is “1” pb_re The p-bus read enable is preferably used to p-bus read validate a read access from a enable memory-mapped memory location (memory, register, FIFO, etc.) by the CPU. Each block has either a pb_re or a pb_rs or both. pb_re is ignored for writes. It is launched on the rising edge of pb_clk and is valid until the next rising edge of pb_clk. A pb_blk_sel is preferably asserted for all cycles where pb_re is “1”, and validates the read enable. pb_rs The p-bus read strobe is preferably used to validate p-bus read a read access from a memory-mapped memory location strobe (memory, register, FIFO, etc.) by the CPU. Each block has either a pb_re or a pb_rs, or both. pb_rs is ignored for writes. It is launched on the falling edge of pb_clk and is valid until the next rising edge of pb_clk. A pb_blk_sel is preferably asserted for all cycles where pb_rs is “1”, and validates the read strobe. The signals, pb_re or pb_rs may be used to trigger any operation that is initiated on a p-bus read, e.g. pb_re may be used to update FIFO pointers on reads. pb_we The p-bus write enable is preferably used to validate a p-bus write write access to a memory-mapped enable memory location (memory, register, FIFO, etc.) by the CPU. Each block has either a pb_we or a pb_ws, or both. pb_we is ignored for reads. It is launched on the rising edge of pb_clk and is valid until the next rising edge of pb_clk. A pb_blk_sel is preferably asserted for all cycles where pb_we is “1”, and validates the write enable. pb_ws The p-bus write strobe is preferably used to validate p-bus write a write access to a memory-mapped memory location strobe (memory, register, FIFO, etc.) by the CPU. Each block has either a pb_we or a pb_ws, or both. pb_ws is ignored for reads. It is launched on the falling edge of pb_clk and is valid until the next rising edge of pb_clk. A pb_blk_sel is preferably asserted for all cycles where pb_ws is “1”, and validates the write strobe. pb_blk_sel The p-bus block select indicates that an access p-bus block to the specified block is valid. select Each block has a select. The selects are generally mutually exclusive (only one asserted at a time), but are not necessarily so. For example, all block- selects will be simultaneously asserted for a broadcast write. pb blk_sel is valid on the rising edge of pb_clk. pb_blk_rdata The p-bus block read data is the data read from a p-bus block memory-mapped memory location (memory, read data register, FIFO, etc.) by the CPU. Each block with memory-mapped locations readable by the CPU has a pb_blk_rdata. It is preferably used only for reads and is ignored for writes. It is valid on the rising edge of pb_clk when a pb_blk_sel is “1”. pb_blk_wait The p-bus block wait is preferably used to generate p-bus block the wait signal to the CPU. The CPU wait signal is wait preferably asserted by the p-bus controller when it decodes an address range which requires a wait or when the block indicates that a wait will be necessary. The CPU wait signal remains asserted until the pb_blk wait is de-asserted indicating that an access is complete. If the access is preferably a write operation, it must be safe for the pb_wdata and associated control signals to be negated on a next rising edge of pb_clk. If the access is preferably a read operation, the data must remain valid on the pb_blk_rdata lines until the next rising edge of pb_clk. Pb_blk_sel, pb_addr and pb_wdata must remain stable from the beginning of a wait cycle until pb_blk_wait is negated. pb_we, pb_ws, pb_re and pb_rs however, are asserted for only one half or one clock signal cycle regardless of wait. This preferable arrangement simplifies FIFO type logic, eliminating the need for peripherals to latch address and data, or to perform an edge detect of the read/write strobes or enables.

The pb_we and pb_ws signals are used to trigger any operation that is initiated on a p-bus write, e.g., pb_we may be used to update FIFO pointers on writes. The pb_we signal is preferably a full clock cycle wide, and pb_ws is only a half clock cycle wide and occurs in the second half of the period. Such preferably allows latch-based embodiments to be easily integrated. The pb_ws signal is only asserted during the second half of the clock signal cycle to allow time for address decode before its qualification with the strobe.

When writing to synchronous registers such as counters that are not static, a full-clock cycle-wide signal (pb_we) is preferably used to enable the register write data. This preferably allows the maximum time for signal propagation to the flip-flop inputs. If a register is implemented with a latch or if a register is implemented with the write strobe as the clock signal input to a flip-flop, the half-clock signal (pb_ws) is preferably used to allow time for the address decode to stabilize before being enabled by the strobe.

When using pb_ws asynchronously to clock a flip-flop or to enable a latch, the address decode logic must not change state while pb_ws is asserted. This can be done by ensuring that an address decode is complete within one-half pb_clk cycle and that a qualification of the address with pb_ws is the last operation done before the result is preferably used as the latch enable or the flip-flop clock signal.

If all reads are from static registers, the pb_re and pb_rs signals may be omitted by using the pb_blk_sel and pb_addr signals alone to generate pb_blk_rdata. If however, the read triggers any operation such as a state machine or FIFO pointer update, either pb_re or pb_rs must be used.

FIGS. 3-8 represent the signal waveforms and timing for a “normally not ready” block which negates pb_blk_wait when not addressed. Signal pb_blk_wait is asserted immediately when being addressed if the access will take more than one cycle. A “normally not ready” block asserts pb_blk_wait when not addressed. It negates pb_blk_wait when it is addressed and the access can be completed in one cycle. Otherwise pb_blk_wait stays asserted. The p-bus controller must ignore pb_blk_wait except when the block “blk” is being accessed.

FIG. 3 represents the signal waveforms and timing for the p-bus write protocol. The signal pb_addr becomes valid on a rising edge of pb_clk. A pb_blk_sel signal is also generated along with pb_addr from the same address inputs. Signal pb_we is preferably asserted on a rising edge of pb_clk. Signal pb_ws is preferably asserted on a falling edge of pb_clk. Signal pb_wdata becomes valid on a rising edge of pb_clk. Signals pb_addr, pb_blk_sel, pb_wdata and pb_rdata may be invalid on a next rising edge of pb_clk when pb_we, pb_ws, pb_re and pb_rs are not asserted and when wait is not active. Signals pb_we and pb_ws are negated on a next rising edge of pb_clk.

FIG. 4 represents the signal waveforms and timing for the p-bus read protocol. Signal pb_addr becomes valid on a rising edge of pb_clk. A pb_blk_sel signal is also generated along with pb_addr from the same address inputs. Signal pb_re is preferably asserted on a rising edge of pb_clk. Signal pb_rs is preferably asserted on a falling edge of pb_clk. The pb_blk_rdata is valid before the next rising edge of pb_clk, and is held-for one flip-flop/latch hold time after the clock signal edge. Signals pb_addr, pb_blk_sel, pb_wdata and pb_rdata may be invalid on a next rising edge of pb_clk when pb_we, pb_ws, pb_re and pb_rs are not asserted and when wait is not active. Signals pb_re and pb_rs are negated on a next rising edge of pb_clk.

FIG. 5 represents the signal waveforms and timing for the p-bus write protocol with asynchronous waits. Signal pb_addr becomes valid on a rising edge of pb_clk. A pb_blk_sel signal is also generated along with pb_addr from the same address inputs. Signal pb_we is preferably asserted on a rising edge of pb_clk. The pb_ws signal is preferably asserted on a falling edge of pb_clk. The pb_wdata becomes valid on a rising edge of pb_clk. If the block requires wait states, pb_blk_wait remains asserted on a next rising edge of pb_clk. Single pb_blk_wait may be held normally true if a wait will always be required. Signal pb_we and pb_ws will be negated on a next rising edge of pb_clk. Signal pb_blk_wait is negated when the write is complete (normally not ready). The trailing edge of pb_blk_wait is synchronized. Signals pb_addr, pb_blk_sel, pb_wdata and pb_rdata may be invalid on a next rising edge of pb_clk when pb_we, pb_ws, pb_re and pb_rs are not asserted and when wait is not active.

FIG. 6 represents the signal waveforms and timing for the p-bus read protocol with asynchronous wait. This protocol illustrates a “normally not ready” system. The p-bus controller will ignore pb_blk_wait except when the block, “blk”, is being accessed. Signal pb_addr becomes valid on a rising edge of pb_clk. A pb_blk_sel signal is also generated along with pb_addr from the same address inputs. Signal pb_re is preferably asserted on a rising edge of pb_clk. Signal pb_rs is preferably asserted on a falling edge of pb_clk. If the block requires wait states, pb_blk_wait remains asserted on a next rising edge of pb_clk. Signal pb_blk_wait may be “normally true” if a wait will always be required. Signal pb rdata is valid before the negation of pb_blk_wait. Signal pb_re and pb_rs will be negated on a next rising edge of pb_clk. Signal pb_blk_wait is negated when the read data is ready. The trailing edge of pb_blk_wait is synchronized. Signals pb_addr, pb_blk_sel, pb_wdata and pb_rdata may be invalid on a next rising edge of pb_clk when pb_we, pb_ws, pb_re and pb_rs are not asserted and when wait is not active.

FIG. 7 represents the signal waveforms and timing for the p-bus write protocol with synchronous wait. This protocol illustrates a “normally not ready” system. The p-bus controller will ignore pb_blk_wait except when the block, “blk”, is being accessed. Signal pb_addr becomes valid on a rising edge of pb_clk. A pb_blk_sel signal is also generated along with pb_addr from the same address inputs. Signal pb_we is preferably asserted on a rising edge of pb_clk. Signal pb_ws is preferably asserted on a falling edge of pb_clk. Signal pb_wdata becomes valid on a rising edge of pb_clk. If the block requires wait states, then pb_blk_wait remains asserted on a next rising edge of pb_clk. Signal pb_blk_wait may be “normally true” if a wait will always be required. Signals pb_we and pb_rs will be negated on a next rising edge of pb_clk. Signal pb_blk_wait is negated when the write is complete and remains negated until the next rising edge of pb_clk. Signals pb_addr, pb_blk_sel, pb_wdata and pb_rdata may be invalid on a next rising edge of pb_clk when pb_we, pb_ws, pb_re and pb_rs are not asserted and when wait is not active.

FIG. 8 represents the signal waveforms and timing for the p-bus read protocol with synchronous wait. This protocol illustrates a “normally not ready” system. The p-bus controller will ignore pb_blk_wait except when the block, “blk”, is being accessed. Signal pb_addr becomes valid on a rising edge of pb_clk. A pb_blk sel signal is also generated along with pb_addr from the same address inputs. Signal pb_re is preferably asserted on a rising edge of pb_clk. Signal pb_rs is preferably asserted on a falling edge of pb_clk. If the block requires wait states, pb_blk_wait remains asserted on a next rising edge of pb_clk. Signal pb_blk_wait may be “normally true” if a wait will always be required. Signal pb_rdata is valid before the first rising edge of pb_clk where pb_blk_wait is negated. The pb_re and pb_rs will be negated on a next rising edge of pb_clk. If the block requires wait states, pb_blk_wait is negated when the read data is ready. Signals pb_addr, pb_blk_sel, pb_wdata and pb_rdata may be invalid on a next rising edge of pb_clk when pb_we, pb_ws, pb_re and pb_rs are not asserted and when wait is not active.

FIG. 9 represents a p-bus interconnection example for a universal asynchronous receiver transmitter (UART) 900. A UART is commonly used for software debug and as a general-purpose communications interface. A standard 16450-type UART is illustrated in FIG. 9. A more complex UART may include a DMA channel, e.g., which interfaces to the m-bus 130 (FIG. 1).

Referring again to FIG. 1, the m-bus supports communication between shared memory and channels or DMA peripherals. It operates synchronous to the MAC 140. The data and address widths are application-specific. Hidden arbitration is preferably used for DMA bus masters with no additional clock signal cycles needed for arbitration. Dynamically variable pipelining is preferably used. The m-bus allows read-modify-write cycles without bus lock. The m-bus 130 is the interface for communication to shared memory through the MAC 140. The processor(s) and other blocks that need to directly access shared memory (DMA) use the m-bus 130. The m-bus 130 is preferably an initiator-target interface, which supports multiple initiators, DMA peripherals (channels), and one target, the MAC 140. The m-bus 130 timings are synchronous with the MAC 140.

The m-bus 130 signals fall into two categories, those that are broadcast from the MAC 140 to all DMA peripherals, and those that are point-to-point between the MAC 140 and a specific DMA peripheral.

TABLE III m-bus signal summary signal direction required timing description mb_clk n/a yes n/a MAC clock mb_blk_req MAC-to- yes early, memory access peripheral first 30% request of clk cycle mb_blk_gnt peripheral yes early, memory access -to-MAC first 30% grant of clk cycle mb_blk_dir peripheral no mid, 1 = memory -to-MAC first 60% write, of clk cycle 0 = memory read, expands to mb_blk_dir [1:0] where ′1x′ = read-modify-write mb_blk_addr peripheral no mid, memory address -to-MAC first 60% of clk cycle mb_blk_size peripheral no mid, size of access, -to-MAC first 60% in bytes of clk cycle mb_blk_wda peripheral yes for early, write data -to-MAC write- first 30% from CPU only and of clk cycle read/write block mb_blk_burst peripheral no early, memory burst -to-MAC first 30% request of clk cycle mb_rdata MAC-to- yes early, memory read data peripheral first 30% of clk cycle mb_blk_qual MAC-to- yes early, memory access peripheral first 30% in progress of clk cycle mb_stb MAC-to- yes early, memory data peripheral first 30% strobe of clk cycle mb_laststb MAC-to- no early, last memory peripheral first 30% data strobe of clk cycle of grant mb_done MAC-to- yes early, memory request peripheral first 30% done of clk cycle mb_incaddr MAC-to- yes early, memory address peripheral first 30% increment of clk cycle

TABLE IV m-bus signal descriptions mb_clk All m-bus 130 signals are synchronous to the mb_clk. m-bus clock It is this clock signal that is preferably used by the MAC 140. This signal may be generated and distributed by the MAC 140, or may be generated by a clock signal control module and distributed to the MAC 140 and other modules. mb_blk_req The memory request signal is preferably m-bus 130 used to indicate that a DMA peripheral wishes to memory access external memory. All DMA peripherals must request provide a memory access request. This signal is preferably asserted when an access to memory is needed and must remain asserted until it completes at least one access. It may be asserted at any time (synchronous with the mb_clk) but may be negated in any clock signal cycle where mb_done is preferably asserted. Memory access will switch immediately to the next requestor. For non-burst transfers, mb_blk_req can be continuously asserted until no more data is needed. For burst transfers, mb_blk_req may be continuously asserted as long as more data is needed, but may be negated only at a burst boundary where mb_done is preferably asserted. If mb_blk_gnt is negated, the DMA peripheral must suspend access to memory, however it may continue to assert mb_blk_req. mb_blk_gnt The memory grant signal is preferably m-bus 130 used to indicate that a DMA memory grant peripheral is granted access to shared memory. A grant is provided to each DMA peripheral. This signal is preferably asserted when access to memory is granted to a DMA peripheral. It may be asserted at any time when mb_blk_req is preferably asserted and may be negated during any clock signal cycle where mb_done is preferably asserted. mb_blk_req may remain asserted if the requestor needs more accesses, however, it must suspend all transactions until mb_blk_gnt is re-asserted. If mb_blk_req is negated, mb_blk_gnt must be negated within the next clock signal cycle. All grants are normally mutually exclusive. Some architectures may benefit from having more than one grant simultaneously asserted, but this is not the usual case. If no requests are asserted, no grant is preferably asserted. The following signals from the MAC 140 are valid to a DMA peripheral only if mb_blk_gnt is preferably asserted: mb_done, mb_incaddr. mb_blk_dir The memory access direction signal indicates whether memory the current access is preferably a memory write access or a memory read. All DMA peripherals that direction read and write external memory must provide a memory access direction. if a block only performs read operations or only performs write operations, this signal may be omitted from the interface. In an ASIC environment, this optimization may save logic. Encoding for mb_blk_dir is described below, mb_blk_dir is expanded to mb_blk_dir[1:0] in a system where read/modify/write is implemented. Without read/modify/write, mb_blk_dir = 0 for a read and 1 for a write. With read/modify/write, mb_blk_dir [1:0] to 00 for a read, 01 for a write, and 10 or 11 for a read/modify/write. This signal must be valid concurrent with or prior to the assertion of mb_blk_req and must remain valid until the access is complete. mb_blk_dir may change from one access to the next without negating mb_blk_req, but may only do so during a cycle where mb_incaddr is preferably asserted. mb_blk_dir is ignored if mb_blk_gnt is not asserted. mb_blk_addr The memory address is the address of the memory to memory be written or read. The start address is preferably address application specific and may be relative to the beginning of shared memory, which may not be the same as the processor memory map address. All DMA peripherals that read or write shared memory must provide a memory address. This signal may be omitted from the interface if the block performs non-data accesses to memory, for example, the refresh DMA peripheral. In an ASIC environment, this optimization may save logic. This signal must be valid concurrent with or prior to the assertion of mb_blk_req. mb_(')blk_addr may change only during a cycle where mb_incaddr is preferably asserted. mb_blk_addr is ignored if mb_blk_gnt is not asserted. mb_blk_size The memory access size is preferably used in systems memory that allow an access to a subset of the bus width, access size for example, byte-write to 32-bit memory. This signal may be omitted for reads, if the entire bus width is preferably always read and the unneeded data ignored. Encoding of the access size may be application specific. The preferred encoding scheme for 32-bit data is mb_blk_size [1:0] of 00/01/10/11 for byte/word/doubleword/quadword. In general (word length = 16 bits), mb_blk_size = log₂(access-size/8), where access-size is in bits and is preferably an element of {2 n, n > 3}. Expanding mb_blk_size to 3 bits accommodates systems with bus widths up to 1024 bits. All DMA peripherals that may write to a subset of the external memory bus width must provide a memory access size. This signal may be omitted from the interface if the block only performs non-data accesses to memory or always accesses the full bus width. In an ASIC environment, this optimization may save logic. This signal must be valid concurrent with or prior to the assertion of mb_blk_req. mb_blk_size may change only during a cycle where mb_incaddr is preferably asserted. mb_blk_size is ignored if mb_blk_gnt is not asserted. mb_blk_size would not typically change during any set of transactions However, if a DMA channel supports writes on any byte boundary, it may be necessary in order to align the accesses when the memory controller does not support misaligned accesses. This can be illustrated with a transfer of 10 bytes to 32-bit memory, starting at address “1”. To complete the operation with a minimum number of accesses, the DMA channel would have to write 1 byte to address “1”, 1 word to address “2”, 1 doubleword to address “4”, 1 word to address “8” and 1 byte to address “10”. In this example, every access is preferably a different size. Mb_blk_burst This signal is preferably used memory burst to inform the MAC 140 that a burst transaction operation is being undertaken. It is preferably asserted concurrent with or prior to the assertion of mb_blk_req and de-asserted in the clock signal cycle where the final mb_done of the burst is preferably asserted. However, if another burst access is requested, it may remain asserted if mb_blk_req remains asserted. If the system implements variable burst lengths-that is, different burst lengths for different requestors, mb_blk_burst can be expanded: mb_blk_burst[2:0] Pre-programmed burst size Variable burst sizes 0 no bursting 000 no bursting 1 fixed-length burst 001 2 accesses per burst 010 4 accesses per burst 011 8 accesses per burst 100 16 accesses per burst 101 32 accesses per burst 110 64 accesses per burst 111 128 accesses per burst The mb_blk_burst signal is optional and is only meaningful if the memory controller and the addressed memories take advantage of it. If asserted, the memory transaction is preferably assumed by the MAC 140 to be for a (pre- programmed) fixed number of accesses and the mb_blk_req signal cannot be negated before that many accesses are complete. For example, SDRAMs can be programmed for fixed burst sizes, on a end of a burst, the SDRAM will automatically precharge allowing for more efficient use of the memory. mb_blk_wdata All DMA peripherals that write to memory write external memory must provide memory data write data. If a block only performs read operations, this signal may be omitted from the interface. In an ASIC environment, this optimization may save logic. This signal must be valid concurrent with or prior to the assertion of mb_blk_req. mb_blk_wdata may change only during a cycle where mb_stb is preferably asserted. mb_blk_wdata is ignored if mb_blk_gnt is not asserted. If a DMA peripheral writes a subset of the bus width (for example, byte write on a 32-bit bus), it will handle endian- ness. For example, for a 32-bit bus width, if the system is big endian, then for a byte write to byte 0, data is placed in the upper 8 bits of mb_blk_wdata. if the system is little endian, the byte is placed in the lower 8 bits of mb_blk_wdata. This is implemented by mirroring the byte across the entire bus. For a 16-bit access, the data is mirrored on the upper and lower 16 bits of mb_blk_wdata. Alternatively, the system may choose a single endian-ness rather than supporting both big and little endian modes. mb_rdata Memory read data is provided to all memory read DMA peripherals that read from data external memory. If a block only performs write operations, this signal may be omitted from its interface. This signal is valid on the rising edge of the mb_clk coincident with mb_stb. mb_stb. mb_rdata may change after this time. The falling edge of mb_stb may also be used to capture mb_rdata if mb_stb is glitch-free (note that, mb_rdata must be valid by the falling edge). Reads from memory may be done across the entire bus width. If a read is done on a subset of the bus width (for example, byte read on a 32-bit bus), the data may be mirrored across the entire bus to accommodate both big and little endian systems. For a 32-bit bus width, if the system is big endian, then a byte read from address 0 is read from the upper 8 bits of mb_rdata. if the system is little endian, the byte is read from the lower 8 bits of mb_rdata. mb_blk_qual The memory access qualifier is memory preferably used to indicate that a DMA access control peripheral has access to the external memory signal bus and that mb_stb and qualifier mb_laststb are valid for that DMA peripheral has access. mb_blk_qual is provided to each DMA peripheral. mb_blk_qual is preferably asserted when data is being transferred between the MAC 140 and a DMA peripheral. All mb_blk_qual signals are normally mutually exclusive. Some architectures may call for more than one access signal to be simultaneously asserted, but this is not the usual case. If no requests are asserted, no qualifiers are issued. mb_stb and These signals from the MAC 140 are valid mb_laststb to a DMA peripheral only if mb_blk_qual is asserted. These signals are ignored at all times when mb_blk_qual is not asserted. In general, there will be at least one clock signal cycle delay from mb_blk_req to mb_blk_gnt. Delay from mb_blk_gnt to the first mb_done is embodiment dependent. If mb_blk_req remains asserted, mb_done may be asserted every clock signal cycle (e.g. synchronous memories) and there is no overhead for any accesses other than the first. mb_done The memory request done indicates that a memory requested memory access has request done been started and the MAC 140 state machines are evaluating whether or not another memory cycle is needed. This signal is preferably used by the DMA peripherals to determine when the request is negated, mb_blk_req negation must be coincident with mb_done. Signal mb_done is broadcast to all DMA peripherals. Each DMA peripheral must qualify the mb_done with its mb_blk_gnt before using it. Signal mb_blk_req is negated with enough setup time so that on a next rising clock signal edge, the MAC 140 state machines have decided whether or not to begin another memory access. Note, too, that due to the pipeline structure of some memories, an access may not be completed until several cycles after mb_done is preferably asserted. mb_incaddr The memory address increment signal is preferably memory used to provide the timing of address changes. address mb_incaddr is broadcast to all DMA increment peripherals and may or may not be coincident with any other signal. Each DMA peripheral must qualify mb_incaddr with its mb_blk_gnt before using it. If mb_blk_burst is preferably asserted, the MAC 140 or accessed memory will automatically increment the address during the burst, thus mb_incaddr can be ignored by a requestor which always performs burst accesses to or from burst-capable memory, such as instruction cache fetches from SDRAM. mb_stb The memory data strobe indicates that data memory data has been written to memory or strobe that memory read data is preferably available. Read data is valid on the falling edge of mb_stb or on the rising edge of the mb_clk coincident with mb_stb. If mb_stb is glitch-free, it may be used to latch mb_rdata if necessary. Signal mb_stb is broadcast to all DMA peripherals. Each DMA peripheral must qualify the mb_stb with its mb_blk_qual before using it. mb_laststb The last memory data strobe indicates that a last memory current mb_stb is the last strobe of the current burst. data strobe If mb_blk_burst is not asserted or, if asserted with non-bursting memory accesses, mb_laststb will be asserted each time that mb_stb is preferably asserted. This signal may be omitted if not needed. mb_laststb is broadcast to all DMA peripherals and is coincident with mb_stb. Each DMA peripheral must qualify the mb_laststb with its mb_blk_qual before using it. mb_laststb may be used by the DMA peripherals to update status. It may also be used to eliminate the need for separate burst Status in the DMA peripheral, saving some logic. Note: The MAC 140 may ignore mb_blk_burst when accessing memories that have no inherent bursting advantage. When accessing non-burst-capable memories, mb_laststb is preferably asserted with each access. For maximum compatibility, a requestor does not assert mb_blk_burst unless accessing burst-capable memories.

The m-bus 130 preferably supports variable pipelining. The pipeline controls are mb_done, mb_incaddr and mb_stb. With these signals separated, it is easier to accommodate many interface timings. Since these control signals are independent, requestors must not make any assumptions about their relative timings. That is, there is no fixed order to their assertion. Because the pipelining is variable, optimized to the timings of the requested memory, multiple m-bus 130 accesses may be started before the data for the first request is preferably available or needed. Similarly, in any given clock signal cycle, the address may be several accesses in advance of the data or the data may be in advance of the address. If the accessed memory is not pipelined (such as flash memory), this condition will not occur.

The separation of controls simplifies the logic embodiment for a requestor, since mb_stb, mb_incaddr and mb_done accompany every access. In a typical system, a DMA channel stores write and read data in a FIFO. The data would be strobed to and from the FIFO using mb_stb, the memory address counter would be updated by mb_incaddr, and the request control logic would operate off of mb_done.

All m-bus 130 signals from the requester to the MAC 140 must be latched if the MAC 140 removes mb_blk_gnt before asserting mb_blk_qual because of the pipelining. This condition may occur if the MAC 140 or accessed memory is heavily pipelined and only a single access is requested. Similarly, the MAC 140 must maintain proper internal pipelining of the requestor's control signals.

In general for a synchronous embodiment, there will be at least one clock signal cycle delay from mb_blk_req to mb_blk_gnt. Delay from mb_blk_gnt to the first mb_done is dependent upon the implementation of the MAC 140 and the type of memory accessed. If mb_blk_req remains asserted, mb_done may be asserted every clock signal cycle and there is no overhead for any accesses except the first, because of the pipelining. Thus, latency is only induced when switching requestors, memory types or access type.

If a requestor only requires a single access per grant, mb_incaddr can be ignored, as it is preferably used for pipeline control only, not access or data control.

When a requestor accesses asynchronous SRAM, the address and write data will be needed on a beginning of the cycle, and remains unchanged until the end of the cycle. Thus mb_done, mb_incaddr and mb_stb would occur on the end of the cycle.

When a requestor accesses EDO DRAM, the address needs to be updated before the end of the cycle in order to provide setup time for the next access. Signal mb_incaddr can occur up to three clock signal cycles before the mb_stb, depending on the embodiment. Due to setup and hold requirements, the address would consistently lead the strobe, effecting a pipeline. Signal mb_done will be asserted anywhere between the mb_incaddr and mb_stb depending on the needs of the controlling state machine. For all accesses of the same type to the same memory, the timing will be constant, however the timing will generally vary between access types (read, write, read/modify/write) and may vary depending upon the access size and burst type.

Implementations of the m-bus 130 and arbiter 142 are application specific. The arbiter 142 takes as input a request from each initiator and responds with a grant. The m-bus 130 implements hidden arbitration, that is, no specific clock signal cycles are dedicated to arbitration. Arbitration will occur when any request is negated and the current memory access is finished. Arbitration type may be round robin, timed, fixed-priority, rotating priority, or others, depending on the needs of the system.

The m-bus arbitration preferably requires that each requestor have a request, mb_blk_req, and a grant, mb_blk_gnt. The mb_blk_req signal may be asserted at any time, but must remain asserted until at least one access has been granted. The mb_blk_req signal must be negated only when an mb_done is received. The mb_blk_gnt signal may be negated at any time. If mb_blk_gnt is negated, mb_blk_req may remain asserted.

Arbiter 142 control signals are necessarily specific to the particular application. Arbitration evaluation may be done using mb_done, or other signals generated by the MAC 140 may be used.

FIG. 10 represents the signal timing for m-bus memory write cycles. Signal mb_blk_dir, mb_blk_size mb_blk_addr and mb_blk_wdata are valid at mb_blk_req assertion. Signal mb_blk_req may not be negated without at least one access. When memory is preferably available mb_blk_gnt is preferably asserted. Signal mb_blk_req is negated during a cycle when mb_done is preferably asserted. Signal mb_blk_addr and mb_blk_size are updated during a cycle where mb_incaddr is preferably asserted. Signal mb_blk_wdata is updated during a cycle where mb_stb is preferably asserted. Signal mb_blk_gnt may be negated before all requested data has been transferred. Signal mb_blk_req may remain asserted. Signal mb_blk_gnt frames all mb_done and mb_incaddr signals corresponding to an access, and mb_blk_qual frames all mb_stb and mb_laststb signals corresponding to an access. Signals mb_incaddr, mb_done, mb_stb, and mb_laststb may be active continuously if each access is completed in one clock signal cycle.

FIG. 11 represents the signal timing for m-bus memory read cycles. Signals mb_blk_dir, mb_blk_size, and mb_blk_addr are valid at mb_blk_req assertion. Signal mb_blk_req may not be negated without at least one access. When memory is preferably available mb_blk_gnt is preferably asserted. Signal mb_blk_req is negated during a cycle when mb_done is preferably asserted. Signals mb_blk_addr and mb_blk_size are updated during a cycle where mb_incaddr is preferably asserted. Signal mb_rdata is valid on a rising edge of mb_clk where mb_stb is preferably asserted. If pipelined memory is preferably used mb_stb may not occur until several clock signal cycles after mb_done. Signal mb_blk_gnt may be negated before all requested data has been transferred. Signal mb_blk_req may remain asserted. Signal mb_blk_gnt frames all mb_done and mb_incaddr signals corresponding to an access, and mb_blk_qual frames all mb_stb and mb_laststb signals corresponding to an access. Signals mb_incaddr, mb_done, and mb_stb may be active continuously if each access is completed in one clock signal cycle.

FIG. 12 represents the signal timing for m-bus memory read-modify-write cycles, where mb_blk_dir is extended to two bits to indicate read, write or read-modify-write operation. For read-modify-write cycles, mb_blk_wdata behavior is modified. Signal mb_blk_wdata is the result of a data mask applied to mb_rdata. Signals mb_blk_dir, mb_blk_size, mb_blk_addr, and mb_blk_wdata are valid at mb_blk_req assertion, mb_blk_req may not be negated without at least one access. When memory is preferably available mb_blk_gnt is preferably asserted. Signal mb_blk_req is negated during a cycle when mb_done is preferably asserted. Signal mb_blk-addr and mb_blk_size are updated in the clock signal cycle where mb_incaddr is preferably active. The data mask is updated in clock signal cycle where mb_stb is preferably active and when signal rb_rdata becomes valid. The data mask must combinationally modify mb rdata in the DMA peripheral since there is no indication to the requestor when the read cycle is complete. The result of the mask is returned as mb_blk_wdata. Signal mb_blk_gnt frames all mb_done and mb_incaddr signals corresponding to an access, and mb_blk_qual frames all mb_stb and mb_laststb signals corresponding to an access. A write cycle is complete when mb_stb or mb_done are asserted, or when mb_stb and mb_done are asserted simultaneously.

FIG. 13 represents the signal timing for m-bus memory write cycles. Signals mb_blk_dir, mb_blk_size, and mb_blk_addr are valid at mb_blk_req assertion. Signal mb_blk_req may not be negated without at least one access. When memory is preferably available mb_blk_gnt is preferably asserted. Signal mb_blk_req is negated during a cycle when mb_done is preferably asserted. Signals mb_blk_addr and mb_blk_size are updated during a cycle where mb_incaddr is preferably asserted. Signal mb_blk_wdata is updated during a cycle where mb_stb is preferably asserted. Signal mb_blk_gnt may be negated before all requested data has been transferred. Signal mb_blk_req may remain asserted. Signal mb_blk_gnt frames all mb_done and mb_incaddr signals corresponding to an access, and mb_blk_qual frames all mb_stb and mb_laststb signals corresponding to an access. Signals mb_incaddr, mb_done, and mb_stb may be active continuously if each access is completed in one clock signal cycle.

FIG. 14 represents the signal timing for m-bus memory burst read cycles. Signals mb_blk_dir, mb_blk_size, mb_blk_addr, mb_blk_burst, and mb_blk_wdata are valid at mb_blk_req assertion. Signal mb_blk_req may not be negated without at least one access. When memory is preferably available mb_blk_gnt is preferably asserted. Signal mb_blk_req is negated during a cycle when mb_done is preferably asserted. Signal mb_blk_addr and mb_blk_size are updated during a cycle where mb_incaddr is preferably asserted. Signal mb_rdata is valid on a rising edge of mb_clk where mb_stb is preferably asserted. If pipelined memory is preferably used mb_stb may not occur until several clock signal cycles after mb_done. Signal mb_gnt may be negated before all requested data has been transferred. Signal mb_blk_req may remain asserted. Signal mb_blk_gnt frames all mb_done and mb_incaddr signals corresponding to an access, and mb_blk_qual frames all mb_stb and mb_laststb signals corresponding to an access. Signal mb_incaddr, mb_done, and mb_stb may be active continuously if each access is completed in one clock signal cycle.

FIG. 15 illustrates an m-bus interconnection 1500. Logic “AND-OR” gates are used instead of multiplexers. This is key to the bus implementation. This promotes design friendliness, enhanced performance and reduces bus loading while eliminating bus turnaround.

The m-bus outputs from the DMA blocks are not qualified, rather they are logically AND'ed with mb_blk_gnt then OR'd together with the m-bus block.

The VSI alliance. (VSIA) on-chip bus (OCB) development working group issued version 1.0 of the on-chip bus attributes specification, OCB 1 1.0. Herein is defined a minimum set of attributes for OCB architectures used to integrate virtual components (VCs).

TABLE V General Attributes technical attribute m-bus p-bus type bus DMA bus peripheral bus address yes - system specific yes - peripheral specific data yes - 8, 16, 128 bits yes - 8, 16, 32 bits transfer width yes - 8, 16, 128 bits yes - 8, 16, 32 bits command yes - read, write, r-m-w yes - read, write lock no - not needed no - only one bus master errors no no - handled by master command no no data no no timing no no broadcast no no status yes yes - wait arbitration yes no request yes no grant yes no pre-empt yes no cache support yes no user specifiable bits yes - user can add signals yes - user can add signals routing no no route type no no split transactions no no burst transactions yes no

TABLE VI Un-Cached Transactions technical attribute m-bus p-bus write unlocked yes yes read unlocked yes yes read locked no no write locked no no address-only yes - idle is possible yes - idle is possible unlocked address-only locked no no write response no no read response no no write no acknowledge no yes - no handshake I/O read no - memory mapped no - memory mapped I/O write no - memory mapped no - memory mapped configuration read no - memory mapped no - memory mapped configuration write no - memory mapped no - memory mapped read-modify-write yes no

TABLE VII Cached transactions technical attribute m-bus p-bus cache read no no cache write no no cache update no no memory read line no no memory write and invalidate no no cache coherency no no

TABLE VIII Interrupts technical attribute m-bus p-bus interrupt no - separate from bus no - separate from bus synchronous n/a n/a asynchronous n/a n/a level n/a n/a edge n/a n/a interrupt acknowledge n/a n/a

TABLE IX Additional Transactions technical attribute m-bus p-bus memory spaces 1 - single memory space 1 - single memory space bus transactions disconnect no - not applicable no - not applicable error no - not applicable no - not applicable retry no - not applicable no - not applicable retract no - not applicable no - not applicable system events reset yes yes initialize no - not needed no - not needed configure no - not needed no - not needed clock signaling yes yes scheme

TABLE X Implementation & Other Attributes technical attribute m-bus p-bus structure number of masters multi-master (no max) single master number of targets 1 - memory controller multi-tar et no max performance 100% usable cycles 100% usable cycles physical implementation maximum masters no maximum single master maximum targets single-slave no maximum average master gate application dependent depends on number of count targets average target gate depends on number of application dependent count masters average master application dependent zero latency average target application dependent target dependent latency average bandwidth application dependent application dependent peak bandwidth width/clock signal width/clock signal dependent dependent dynamic bus sizing no no device width - target 8,16, ″ 128 bits 8,16,32 bits (scaleable) device width - 8,16, ″ 128 bits 8,16,32 bits master (scaleable) synchronous yes - to rising edge clock yes - to rising edge clock signal signal byte replication no yes data bus distributed and/or distributed and/or implementation timing guidelines yes (early, mid, late) yes (early, mid, late) DMA peripheral yes no transfers address pipelining yes - decoupled no address/data overlapped read/ yes - decoupled read/ no write write data buses late master abort no no read word address no no guarded transfers no no compressed no no transfers ordered transfers no no target busy signals no yes - wait master latency no no signals no tri-states yes yes positive edge clock yes yes signaling only power down n/a n/a

Implementations of the present invention can include the two main processor architectural types, Von Neumann and Harvard. The Von Neumann architecture uses one bus for instruction fetches and data operations. A Harvard architecture uses separate buses to carry instruction fetches and data operations, and so these can operate simultaneously. Most digital signal processors use the Harvard architecture. Embodiments of the present invention can use either processor architecture and multiple processors. A switched channel memory controller can be used for concurrent communication between different DMA devices and internal or external memories, when bandwidth is critical and multiple shared memories are needed.

Embodiments of the present invention are channel based, and so can accommodate multiple clock signal domains with synchronization FIFOs that allow speed matching without loss of throughput.

A common embodiment of the present invention embeds a single Von Neumann processor with application-specific peripherals. Typical applications include games, organizers, appliances and network controllers. Since a Von Neumann processor uses the same bus for instruction and data operations, FIG. 16 shows a processor's external bus connected to both a p-bus controller, for access to the peripherals, and to a cache, or m-bus bridge if no cache is needed for access to shared memory. Memory accesses are made for data and instructions.

When large amounts of time-critical data processing need to be done by a processor, a system as illustrated in FIG. 17 can be implemented with a single Harvard architecture processor. Typical applications include image processors and servo controllers. Both of a processor's external buses are connected to dedicated memory. A p-bus controller is connected to a data bus only since the processor never fetches instructions across the p-bus. Both the instruction bus and data bus are connected to a cache for access to shared memory (or m-bus bridge if no cache is needed). Additional channels can be added to a memory access controller for a second CPU bus without requiring changes.

FIG. 18 shows a dual processor application. Many systems require both time-critical data processing and significant peripheral control. In these systems, a dual-processor implementation can be advantageous. A Von Neumann processor is preferably used for control functions, since these processors are more compact than Harvard architecture processors. A Harvard architecture processor is preferably used for data processing. Typical dual-processor applications include cellular phones, digital cameras and graphics processing. The peripherals used by the control processor are independent of those used by the data processor. Thus, the system is implemented with two p-buses. Additional channels can be added to the memory access controller for the control processor.

FIG. 19 represents embodiments of the present invention with dual processors and a shared p-bus. Either processor can use peripherals, and a p-bus controller with arbitration is preferably used. Access to shared peripherals is controlled using software, for example via semaphores.

FIG. 20 represents a standard memory controller. Switched channel memory controller embodiments of the present invention, as illustrated in FIGS. 21 and 22, are possible which allow multiple DMA devices (and processors) to simultaneously communicate with multiple output channels. These output channels can be connected to external memory, internal memory, or non-DMA blocks. As with a standard memory controller, any DMA peripherals and CPUs supply a request and an address to a switched channel memory controller. However, the address includes both the port, device or memory bank address, and the requested memory location address. Once a requested port, device or bank is free, the requesting DMA or CPU is granted access and can begin transferring data. While data transfer is in progress on the requested port, another DMA peripheral or CPU can simultaneously transfer data to a different port for almost limitless bandwidth, while requiring minimal changes to the rest of the system.

A switched channel memory controller can be configured to allow particular DMAs or CPUs to-access only certain channels. For example, a CPU instruction bus can be connected to an external flash memory through one channel, or an external SDRAM memory through another channel. DMA peripherals are connected to the channel with an external SDRAM. The CPU fetches instructions from the flash memory at the same time that a DMA device is accessing the external SDRAM. But if the CPU is fetching information from the SDRAM, the DMA peripheral will have to wait to communicate to the SDRAM channel.

Switched channel memory controller embodiments of the present invention operate with almost limitless bandwidth. For example, a system embodiment with a 32-bit p-bus and a 32-bit external single data rate (SDR) SDRAM running at one-hundred MHz gives eight-hundred MB/s of available bandwidth on chip. That is four-hundred MB/s available on the p-bus and four-hundred MB/s on the m-bus.

In FIG. 21, adding a separate port for 32-bit external flash memory gives 1.2 GB/s of total on chip bandwidth at one-hundred MHz. That is four-hundred MB/s on the p-bus, plus four-hundred MB/s on each of the m-bus ports. Adding a 128-bit internal dual-port RAM channel and changing from a SDR SDRAM to a double data rate (DDR) SDRAM 64-bit DIMM channel, yields four GB/s of bandwidth at one-hundred MHz. That is four-hundred MB/s on the p-bus, four-hundred MB/s on the flash memory port, plus 1.6 GB/s on each of the other m-bus ports. It is possible to select the necessary bandwidth for an application without having to resort to extremely wide bus widths or running at very high frequencies.

FIG. 22 represents a switched channel memory controller. The changes to the earlier examples that are required to implement this structure are minimal. A switched channel memory controller with two ports is implemented so that two buses of a processor can simultaneously access memory. A flash memory port is dedicated for code execution, while an SDRAM is shared among all DMA peripherals and both processor buses. The processor must arbitrate with the DMA peripherals and even its own data bus any time it is executing from shared memory with a non-switched memory controller. Shared memory arbitration is a bottleneck to maximum processor throughput.

A common strategy for-eliminating such bottlenecks is to use a dedicated internal memory for code execution. For systems with very little dedicated on-chip execution RAM, using a switched channel memory controller also removes the bottleneck, at the expense of needing-more chip pins.

FIG. 23 represents a switched channel memory controller with dual processors in a more complex example where the two processors each have an on-chip dual-port RAM. A switch allows execution by either processor from off-chip flash memory. Data may be transferred to or from a dual-port RAM by a DMA peripheral, or the CPU for processing by the DSP. Or data may be transferred to or from the SDRAM for CPU processing.

With a switched channel memory controller, the CPU can execute from flash memory while simultaneously processing data from a DMA peripheral in the SDRAM. The DSP can at the same time process data from the dual-port RAM while another peripheral is transferring data to or from the RAM. With a switched channel memory controller, no changes to any blocks except the memory controller are needed for the processors and DMA peripherals to take best advantage of the available bandwidth.

Embodiments of the present invention are preferably able to run with different parts of a system running at different frequencies without having to change the CPU or peripheral interfaces. A synchronized FIFO can be interfaced to the memory controller to implement such. With the use of FIFOs, there is no need to redesign the peripheral device interface when the peripheral is moved to another system.

In a fully synchronous system, DMA channels are synchronous to the peripheral and the memory controller. However, FIFO's are needed to obtain best system performance if DMA peripherals are not operating on a same frequency as the memory controller clock signal.

A synchronizing FIFO is preferably used where a peripheral clock signal is asynchronous to the memory controller, or where the peripheral clock signal is synchronous but in a different time domain. A synchronized FIFO is preferably used where the peripheral is operating synchronous to the memory controller, but at a lower speed, e.g., half the speed. For example, if the memory access controller is operating with one-hundred MHz clock, a PCIbus DMA device operating at sixty-six MHz requires a synchronizing FIFO.

In a system poorly suited for synchronizing FIFOs, it would ordinarily be necessary to redesign the PCIbus interface to run at one-hundred MHz. But because channel interfaces are inherent to embodiments of the present invention, this is not necessary. A synchronizing FIFO would typically be necessary if the PCIbus interface were operating at one-hundred MHz, but was clock signaled by a different clock signal tree than the memory controller, and it was not possible to manage the clock signal skews between the two clock signal trees.

A synchronizing FIFO is preferably used when a peripheral clock signal is generated from a memory controller clock signal, or vice versa, and the clock signal skews are well managed. For example, if a memory access controller is running at one-hundred MHz and an Ethernet MAC clock signal is running at half the frequency of the memory controller clock signal, a synchronized FIFO would be used.

Devices with different interfaces can be mixed and matched within the embodiments of the present invention by using a channel to the m-bus (or p-bus) whose interface matches the peripheral. Channel interfaces can be adapted to resemble many peripheral interfaces. Channel interfaces can be adapted so that IP blocks do not need to be modified.

FIG. 24 represents a system without a processor interface to shared memory. Embodiments of the present invention are not limited to implementations with a CPU and shared memory. Any system with a shared resource, e.g., a PCIbus interface, can be used. Similarly, a processor is needed only if the device is programmable. If none of the peripherals are programmable, or if they are programmed through a sequencer, no processor is needed. FIG. 24 illustrates a system embodiment that uses a CPU for configuration only. Such an implementation would be suited for many consumer products.

FIG. 25 illustrates a system embodiment that requires no CPU, but implements a shared controller for communication with a shared external bus. Applications include I/O cards and switching devices.

FIG. 26 illustrates an embodiment with a sequencer for peripheral configuration and control. Such applications include switching devices or a storage controller.

In general, embodiments of the present invention differ significantly from conventional on-chip buses. Point-to-point signals and multiplexing are used instead of shared tri-stated lines to deliver higher performance while simultaneously reducing system and verification time. Typically, the architecture is characterized by two-hundred sixty-four MB/s bandwidth at sixty-six MHz, support for 32-bit, 16-bit, and 8-bit peripherals, separate peripheral I/O and DMA buses, simple protocol for reduced gate count, positive-edge clock signaling only, no tri-state signals or bus holders, low-capacitive loading for high-frequency operation, support for latch based slave peripherals for low power devices, hidden arbitration for DMA bus masters, single clock signal cycle data transfers, etc.

A distinctive feature of embodiments of the present invention is the separation of I/O and memory transfers onto different buses. A p-bus provides an I/O backplane and allows a processor to configure and control peripherals. An m-bus provides a direct memory access (DMA) connection from peripherals to main memory, allowing peripherals to transfer data directly without processor intervention.

FIG. 27 represents a bus structure for a system using the ARM7 processor core. The main embodiment functional units are a p-bus peripheral bus, an m-bus DMA bus with pipelined address, data and control, a p-bus controller which interfaces the processor local bus to p-bus, peripherals connected to the p-bus, DMA peripherals connected to the m-bus, and a memory access controller that connects the m-bus to shared memory. On-chip memory and cache blocks are preferred in most system embodiments.

The separation of I/O and memory traffic onto a p-bus and an m-bus, respectively, has several advantages over single bus systems. Signaling can be point-to-point because on a p-bus there is only one master (the p-bus controller) and multiple slaves (the peripherals), while on an m-bus there are multiple masters (the peripherals) and only a single slave (the memory access controller). In contrast, a PCIbus system must support multiple masters and slaves on a single backbone. This requires a complex protocol that adds overhead in terms of both gates and embodiment time.

For example, a PCIbus must support split transactions largely to prevent CPU accesses to slave peripherals from blocking DMA transfers from bus mastering peripherals. In preferred embodiments, split transaction support is not needed because the slave I/O is confined to the p-bus and does not interfere with DMA transfers on the m-bus.

FIG. 28 shows a PCIbus architecture. Although FIG. 27 is drawn using a conventional bus paradigm, embodiments of the present invention preferably use a star-shaped topology. The broadcast signals that are driven by the p-bus controller and MAC are connected to all their respective peripherals. The signals specific to each peripheral are point-to-point. The bus standard does not define signals from peripheral-to-peripheral that are application specific.

In practical systems, most peripherals exchange only control or status information between peripherals, and do not need to exchange data directly with their peers. Data is instead communicated through main memory using either programmed I/O or DMA. The present invention exploits this to simplify the bus architecture and avoid tri-state signals. In contrast, traditional buses such as a PCIbus are symmetrical in the sense that they may allow any master to talk directly to any slave. This complicates the bus in order to deliver a feature that is usually not used in real systems.

The exclusive use of point-to-point and broadcast signaling increases bus utilization efficiency because there is no need for turn around cycles. Load capacitances are lower because each signal has only a single driver, and only a single load for point-to-point signals. Broadcast signals can easily be re-driven by simple buffers with no extra control logic. Power consumption is reduced because conventional bus holders that oppose signal transitions are eliminated. As a result, the buses can be run at higher speed and with greater efficiency.

The p-bus provides a simple way to connect slave peripherals to the CPU. It uses a simple non-pipelined protocol and supports both synchronous and asynchronous slave peripherals. Bus clock signal-frequency is preferably application and technology specific, and can easily-reach up to one-hundred MHz with 0.35-micron technology. The p-bus can support peripheral data widths of 8-bits, 16-bits, or 32-bits, and the number of address bits connected to each block is defined by the address space required. The p-bus controller is the only bus master and performs centralized address decoding to generate a dedicated select signal to each peripheral.

The p-bus protocol and signaling permit easy memory-mapped register control common to ASIC control. The common tasks of writing and reading registers can be accomplished with a small number of logic gates and minimal verification time. Synthesis and static timing analysis are straightforward because all signals are launched and captured by rising edges of the bus clock signal, and are not bi-directional. Peripherals can be operated at different clock signal frequencies than the p-bus controller by including a wait signal. This simplifies peripheral embodiments and integration by isolating clock signal domains. The p-bus is preferably also designed with low power consumption in mind. Special provisions are provided to ease the integration of peripherals that, though synchronous, use latches for lower power consumption.

The m-bus connects the CPU and DMA-capable peripherals to a main memory via the MAC. The bus clock signal frequency is preferably application and technology specific, and can reach to one-hundred MHz using 0.35 micron technology. The m-bus uses pipelined address and data and hidden arbitration and can support peripheral data widths of 8-bits, 16-bits, or 32-bits. The MAC is the only slave on the bus, all cycles are initiated by the CPU or other DMA peripherals.

The m-bus protocol is optimized both for ASIC-type implementations and for data transfers to and from memory devices. Control signals that are commonly needed for DMA-type transfers are central to the protocol, eliminating the need for bus protocol state machines. The m-bus uses hidden arbitration to further simplify its protocol. However, recognizing that ASICs have a wide range of system requirements, the arbitration scheme is preferably application specific. Because memory devices vary significantly in their protocols and access latencies, the m-bus provides to be adaptive, allowing the MAC to control the bus as it sees fit for the memory device being accessed. This preferably allows optimizations to be made in the MAC to maximize throughput and minimize latency, or for cost-sensitive applications, to minimize embodiment size.

The time required to connect system-on-chip components together and to start system-level simulation can be significantly reduced by standardizing bus interfaces. This greatly simplifies the task of hooking the blocks together. Chip designers can specify which blocks they require and press a button to generate the top level RTL code. This saves time and prevents wiring errors that can take hours to debug in simulation.

The various embodiments of the present invention are preferably a silicon-proven on-chip bus architecture that has significant advantages compared with other system interconnect schemes. Its definition is preferably optimized for ASIC implementations. Its shared-memory architecture is optimized for devices with high bandwidth data streams requiring extensive DMA. This covers a wide range of applications such as mass storage, networking, printer controllers, and mobile communications. Many embodiments are synthesis friendly and provide “plug and play” connectivity to reduce silicon embodiment time.

Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that this disclosure is not interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that all appended claims be interpreted as covering all alterations and modifications as falling within the true spirit and scope of the invention. 

What is claimed is:
 1. An on-chip interconnection system, comprising: a single semiconductor integrated circuit (IC); a plurality of uni-directional buses disposed in the IC; a peripheral-bus (p-bus) included in the plurality of uni-directional buses and that uses a simple non-pipelined protocol and supports both synchronous and asynchronous slave peripherals; a p-bus controller connected to the p-bus and constituting an only bus-master, and including a centralized address decoder for generating a dedicated peripheral select signal, and providing for a connection to synchronous and asynchronous slave peripherals, and further providing for an input/output (I/O) backplane that allows a processor to configure and control any of its slave peripherals; and an m-bus included in the plurality of uni-directional buses, and for providing a direct memory access (DMA) connection from any said slave peripherals to a main memory and permits peripherals to transfer data directly without processor intervention.
 2. The on-chip interconnection system of claim 1, wherein, there are included no tri-stated-buses, and no bi-directional buses.
 3. The on-chip interconnection system of claim 1, wherein, each signal has only a single buffer driver.
 4. The on-chip interconnection system of claim 1, wherein, any broadcast signals are re-driven by simple buffers with no extra control logic.
 5. The on-chip interconnection system of claim 1, wherein, only a single load is presented for point-to-point signals.
 6. The on-chip interconnection system of claim 1, wherein, any included peripherals exchange only control and status information, and do not directly exchange data between themselves.
 7. The on-chip interconnection system of claim 1, wherein, any data to be exchanged between peer peripherals is communicated through main memory using either programmed input/output (I/O) and direct memory access (DMA) transfer cycles.
 8. The on-chip interconnection system of claim 1, wherein, an exclusive use of point-to-point and broadcast signaling provides for increased bus.utilization efficiency that result from an elimination of bus-direction turn-around cycles.
 9. The on-chip interconnection system of claim 1, wherein, the p-bus includes a protocol and signaling method that permit memory-mapped. ASIC-type register control.
 10. The on-chip interconnection'system of claim 1, wherein, all signals are launched and captured on a rising edge of a bus clock signal.
 11. The on-chip interconnection system of claim 1, wherein, any connected peripherals are operated at a clock signal frequency that differs from one used by the p-bus controller by including a wait signal.
 12. The on-chip interconnection system of claim 1, wherein, the p-bus includes logic latches for lower power consumption.
 13. The on-chip interconnection system of claim 1, wherein, the m-bus connects a CPU and any DMA-capable peripherals to a main memory via a memory access controller (MAC).
 14. The on-chip interconnection system of claim 1, wherein, the m-bus includes the use of pipelined address and data, and further includes hidden bus arbitration.
 15. The on-chip interconnection system of claim 13, wherein, said MAC is the only slave on the m-bus bus, and all m-bus transfer cycles are initiated by said CPU and DMA-capable peripherals.
 16. The on-chip interconnection system of claim 13, wherein, the IC is an application specific integrated circuit (ASIC). 